Classification and type material

Basal sauropodomorph phylogeny simplified after Yates, 2007.[25] This is only one of many proposed cladograms for basal sauropodomorphs. Some researchers do not agree that plateosaurs were the direct ancestors of sauropods

Plateosaurus is a member of a group of early herbivores known as "prosauropods".[26] The group name is obsolete, as "Prosauropoda" is not a monophyletic group (thus given in quotation marks), and most researchers prefer the term basal sauropodomorph.[27][28]Plateosaurus was the first "prosauropod" to be described,[26] and gives its name to the family Plateosauridae Marsh, 1895 as the type genus.[29] Initially, when the genus was poorly known, it was only included in Sauria, being some kind of reptile, but not in any more narrowly defined taxon.[15] In 1845, von Meyer created the group Pachypodes (a defunct junior synonym of Dinosauria) to include Plateosaurus, Iguanodon, Megalosaurus and Hylaeosaurus.[30] Plateosauridae was proposed by Othniel Charles Marsh in 1895 within Theropoda.[31] Later it was moved to "Prosauropoda" by von Huene,[32] a placement that was accepted by most authors.[3][16][33][34] Before the advent of cladistics in paleontology during the 1980s, with its emphasis on monophyletic groups (clades), Plateosauridae was defined loosely, as large, broad-footed, broad-handed forms with relatively heavy skulls, unlike the smaller "anchisaurids" and sauropod-like "melanorosaurids".[35] Reevaluation of "prosauropods" in light of the new methods of analysis led to the reduction of Plateosauridae. For many years the clade only included Plateosaurus and various junior synonyms, but later two more genera were considered to belong to it: Sellosaurus[36] and possibly Unaysaurus.[37] Of these, Sellosaurus is probably another junior synonym of Plateosaurus.[16]

The type series of Plateosaurus engelhardti included "roughly 45 bone fragments",[F] of which nearly half are lost.[G] The remaining material is kept in the Institute for Palaeontology of the University of Erlangen-Nuremberg, Germany.[H] From these bones, German palaeontologist Markus Moser in 2003 selected a partial sacrum (series of fused hip vertebrae) as a lectotype.[I] The type locality is not known for certain, but Moser attempted to infer it from previous publications and the colour and preservation of the bones. He concluded that the material probably stems from the "Buchenbühl", roughly two kilometres (1.2 mi) south of Heroldsberg.[J]

Etymology

P. engelhardti in Sauriermuseum, Frick

The etymology of the name Plateosaurus is not entirely clear. Moser pointed out that the original description contains no information, and various authors have offered differing interpretations.[L] German geologist Hanns Bruno Geinitz in 1846 gave "(πλατυς, breit)" [English: broad][M] In the same year, Agassiz offered Ancient Greekπλατη (platê – "paddle", "rudder"; Agassiz translates this as Latinpala = "spade") and σαυρος (sauros – "lizard").[N] Agassiz consequently renamed the genus Platysaurus,[O] probably from Greek πλατυς (platys – "broad, flat, broad-shouldered"), creating an invalid junior synonym. Later authors often referred to this derivation, and the secondary meaning "flat" of πλατυς, so that Plateosaurus is often translated as "flat lizard". Often, claims were made that πλατυς is supposed to have been intended as a reference to flat bones, for example the laterally flattened teeth of Plateosaurus,[P] but the teeth and other flat bones such as the pubic bones and some skull elements were unknown at the time of description.[43]

In 1855, von Meyer published a detailed description of Plateosaurus with illustrations, but again gave no details on the etymology. He repeatedly referred to its gigantic size ("Riesensaurus" = giant lizard) and massive limbs ("schwerfüssig"), comparing Plateosaurus to large modern land mammals, but did not describe any important features that fit the terms "flat" or "shaped like an oar."[Q][43]

In addition to his formal scientific descriptions, von Meyer also gave a public lecture about fossil reptiles in 1851 that included a short mention of Plateosaurus. That talk and a later one on fossil mammals were turned into a general audience book published in 1852, entitled Über die Reptilien und Säugethiere der verschiedenen Zeiten der Erde [On the Reptiles and Mammals from the Different Time Periods of the Earth].[45] In the German text (page 44), von Meyer briefly described Plateosaurus and mentioned that it had "breite, starke Gliedmaassenknochen," which translates as "broad, strong limb bones." Because his original description of Plateosaurus in 1837 stressed the similarity of its large limb bones to those of Megalosaurus and Iguanodon, a meaning "broad lizard" for the name Plateosaurus to refer in particular to its robust limb bones would seem plausible.